<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
<title></title>
</head>

<body>
<script type="text/javascript">
var t = 20;
var b = 30;
var height = 20;
var area = (t+b)*height/2;
document.write("梯形稻田的面积为"+area+"平方米");
</script>
</body>
</html>
